Geochemical, Geophysical Genesis of the Ranggu Geothermal Spring in Aba Prefecture, Western Sichuan: Evidence from Hydrogeochemical and Geophysical Exploration

Geothermal resource is a clean, low-carbon, abundant, safe and high-quality renewable energy. Vigorously developing and utilizing geothermal resources is of great significance to the implementation of the strategic goal of "carbon peak, carbon neutral". Located in Rangtang County, Aba Prefecture, western Sichuan on the southeast edge of the Qinghai-Tibet Plateau, Ranggu geothermal spring is a high-quality geothermal resource drilled in the geothermal resource blank area of the Songpan-Ganzi fold zone. The wellhead water temperature is 39.5℃, and the artesian flow is 1500 m³/d. It is a high-quality thermal mineral water rich in metasilicic acid, metaborate, strontium, fluorine and lithium, and has high medical value. Based on the study of hydrogeochemical and geophysical characteristics, the paper discusses the formation mechanism of geothermal energy. The results show that the pH value of the spring is 6.7~7.1, the total dissolved solids are 2050~2760 mg/L, the hydrochemical type is HCO₃-Na, and the water-rock interaction is intense. Its hydrogen and oxygen isotopes are distributed near the global atmospheric precipitation equation line, indicating that geothermal water is mainly recharged by atmospheric precipitation. The Na-K-Mg balance diagram shows immature water, indicating that the geothermal water is intensely mixed by fissure phreatic water or surface cold water. Based on the traditional geothermal temperature scale, silicon enthalpy mixing model and Cl⁻ correction, it is estimated that the reservoir temperature is 138~183.3℃, and the mixing ratio of cold water is 77.9~84.3%. Based on the characteristics of geophysical exploration and drilling exposure, a conceptual model of the genesis of the Ranggu geothermal spring is constructed in this paper, which can provide theoretical support for the development and utilization of the Ranggu geothermal spring.